Referring to FIG. 1, a conventional cleaning device for fish tank includes an outlet pipe 11, an air suction and exhaust member 12 connected to one end of the outlet pipe 11, a connecting pipe 13 with one end connected to the other end of the outlet pipe 11, and a hood 14 connected to the other end of the connecting pipe 13. The hood 14 of the cleaning device has a bottom open end 141 vertically disposed on gravel (A) above the bottom of the fish tank. While operating the member 12, waste material and water on the gravel (A) is drawn out through the hood 14, the connecting pipe 13, and the outlet pipe 11 by siphonic action. The hood 14 can be moved to every part on the gravel (A) for cleaning waste material thereon.
The conventional cleaning device for cleaning a fish tank draws a lot of water out of the tank and weak suction is provided by siphonic action to make the device truly effective. When more than a third of all water in the fish tank is removed and replaced with fresh water, the fish have a hard time adapting to a new environment and often die as a result. The weak suction fails to remove waste material under or among the gravel stones and the fish tank can not be completely cleaned.
So that it is inconvenient and inefficient to use a conventional cleaning device for cleaning a fish tank.